Previous studies performed in our laboratory indicate that the blood levels of antigen following airway exposure were greater in rabbits with inflamed lungs and were reduced in immunized animals. This information, along with preliminary studies on isolated rabbit lungs, suggests that: (1) Differences in blood levels of antigen following exposure may indicate differences in the rate of uptake through the lung; (2) the primary route of uptake may be from the airways into pulmonary-capillary blood; and (3) inflammation may increase antigen absorption across the lung, and immunization may inhibit absorption. In this project we intend to evaluate these hypotheses and to gain insight into the mechanisms involved. We will determine the rate of I125-ovalbumin (I125-OA) appearance in the blood and the whole body distribution of I125 following aerosol administration in anesthetized rabbits, and the rate of absorption of I125-OA through isolated blood-perfused lungs. Normal rabbits, rabbits with inflamed lungs and OA-immunized rabbits with normal or inflamed lungs will be compared. The antibody class responsible for suppressing the appearance of I125-OA in the circulation will be determined by comparing the rate of I125-OA uptake and the whole body distribution in rabbits which have been passively immunized with anti-OA serum which has been pretreated using class-specific antisera produced against rabbit immunoglobin.